Two years ago, Nina Jankowicz briefly led an agency at the Department of Homeland Security created to fight disinformation — the establishment of which provoked a political and legal battle over the government’s role in policing lies and other harmful content online that continues to reverberate.

Now she has re-entered the fray with a new nonprofit organization intended to fight what she and others have described as a coordinated campaign by conservatives and others to undermine researchers, like her, who study the sources of disinformation.

Already a lightning rod for critics of her work on the subject, Ms. Jankowicz inaugurated the organization with a letter accusing three Republican committee chairmen in the House of Representatives of abusing their subpoena powers to silence think tanks and universities that expose the sources of disinformation.

“These tactics echo the dark days of McCarthyism, but with a frightening 21st-century twist,” she wrote in the letter on Monday with the organization’s co-founder Carlos Álvarez-Aranyos, a public-relations consultant who in 2020 was involved in efforts to defend the integrity of the American voting system.

The inception of the group, the American Sunlight Project, reflects how divisive the issue of identifying and combating disinformation has become as the 2024 presidential election approaches. It also represents a tacit admission that the informal networks formed at major universities and research organizations to address the explosion of disinformation online have failed to mount a substantial defense against a campaign, waged largely on the right, depicting their work as part of an effort to silence conservatives.

Taking place in the courts, in conservative media and on the Republican-led House Judiciary Select Subcommittee on the Weaponization of the Federal Government, the campaign has largely succeeded in eviscerating efforts to monitor disinformation, especially around the integrity of the American election system.

Many of the nation’s most prominent researchers, facing lawsuits, subpoenas and physical threats, have pulled back.

“More and more researchers were getting swept up by this, and their institutions weren’t either allowing them to respond or responding in a way that really just was not rising to meet the moment,” Ms. Jankowicz said in an interview. “And the problem with that, obviously, is that if we don’t push back on these campaigns, then that’s the prevailing narrative.”

That narrative is prevailing at a time when social media companies have abandoned or cut back efforts to enforce their own policies against certain types of content.

Many experts have warned that the problem of false or misleading content is only going to increase with the advent of artificial intelligence.

“Disinformation will remain an issue as long as the strategic gains of engaging in it, promoting it and profiting from it outweigh consequences for spreading it,” Common Cause, the nonpartisan public interest group, wrote in a report published last week that warned of a new wave of disinformation around this year’s vote.

Ms. Jankowicz said her group would run advertisements about the broad threats and effects of disinformation and produce investigative reports on the backgrounds and financing of groups conducting disinformation campaigns — including those targeting the researchers.

She has joined with two veteran political strategists: Mr. Álvarez-Aranyos, formerly a communications strategist for Protect Democracy, a nonpartisan group that seeks to counter domestic authoritarian threats, and Eddie Vale, formerly of American Bridge, a liberal group devoted to gathering opposition research into Republicans.

The organization’s advisory board includes Katie Harbath, a former Facebook executive who was previously a top digital strategist for Senate Republicans; Ineke Mushovic, a founder of the Movement Advancement Project, a think tank that tracks threats to democracy and gay, lesbian and transgender issues; and Benjamin Wittes, a national security legal expert at the Brookings Institution and editor in chief of Lawfare.

“We need to be a little bit more aggressive about how we think about defending the research community,” Mr. Wittes said in an interview, portraying the attacks against it as part of “a coordinated assault on those who have sought to counter disinformation and election interference.”

In the letter to congressional Republicans, Ms. Jankowicz noted the appearance of a fake robocall in President Biden’s voice discouraging voters in New Hampshire from voting in the state’s primary and artificially generated images of former President Donald J. Trump with Black supporters, as well as renewed efforts by China and Russia to spread disinformation to American audiences.

The American Sunlight Project has been established as a nonprofit under the section of the Internal Revenue Code that allows it greater leeway to lobby than tax-exempt charities known as 501(c)(3)s. It also does not have to disclose its donors, which Ms. Jankowicz declined to do, though she said the project had initial commitments of $1 million in donations.

The budget pales in comparison with those behind the counteroffensive like America First Legal, the Trump-aligned group that, with a war chest in the tens of millions of dollars, has sued researchers at Stanford and the University of Washington over their collaboration with government officials to combat misinformation about voting and Covid-19.

The Supreme Court is expected to rule soon in a federal lawsuit filed by the attorneys general of Missouri and Louisiana accusing government agencies of using the researchers as proxies to pressure social media platforms to take down or restrict the reach of accounts.

The idea for the American Sunlight Project grew out of Ms. Jankowicz’s experience in 2022 when she was appointed executive director of a newly created Disinformation Governance Board at the Department of Homeland Security.

From the instant the board became public, it faced fierce criticism portraying it as an Orwellian Ministry of Truth that would censor dissenting voices in violation of the First Amendment, though in reality it had only an advisory role and no enforcement authority.

Ms. Jankowicz, an expert on Russian disinformation who once served as an adviser to Ukraine’s Ministry of Foreign Affairs, stepped down shortly after her appointment. Even then, she faced such a torrent of personal threats online that she hired a security consultant. The board was suspended and then, after a short review, abolished.

“I think we’re existing in an information environment where it is very easy to weaponize information and to make it seem sinister,” Mr. Álvarez-Aranyos said. “And I think we’re looking for transparency. I mean, this is sunlight in the very literal sense.”

Ms. Jankowicz said that she was aware that her involvement with the new group would draw out her critics, but that she was well positioned to lead it because she had already “gone through the worst of it.”